Previously, it has been shown that the addition of a strong acid (such as sulfonic acid) to the process of preparing a polyalkenyl derivative of an unsaturated acidic reagent results in a faster rate of reaction, higher conversion, less tar, and a lower succinic ratio.
U.S. Pat. No. 3,819,660, titled "Alkenylsuccinic Anhydride Preparation," discloses the suppression of fumaric acid sublimation and tar formation during reaction of a 168 to 900 molecular weight alkene with maleic anhydride and increased yield of alkenylsuccinic anhydride by using a catalytic amount of p-alkylbenzenesulfonic acid.
U.S. Pat. No. 4,235,786, titled "Process for Producing Oil-Soluble Derivatives of Unsaturated C.sub.4 -C.sub.10 Dicarboxylic Acid Materials," discloses the Ene reaction of an unsaturated C.sub.4 -C.sub.10 dicarboxylic acid and a C.sub.30 -C.sub.700 olefin carried out in the presence of an oil-soluble, strong organic acid having a pKa of less than 4, such as sulfonic acid.
U.S. Pat. No. 5,777,025, titled "Process for Preparing Polyalkenyl Substituted C.sub.4 to C.sub.10 Dicarboxylic Acid Producing Materials," discloses a process for preparing a polyalkylene derivative of a monounsaturated C.sub.4 carboxylic acid by running the reaction in the presence of a sediment-inhibiting amount of an oil-soluble hydrocarbyl substituted sulfonic acid.
European Patent Application 0 542 380 A1, titled "Process for the preparation of polyalkenyl derivatives of unsaturated dicarboxylic acid materials," discloses a process for the preparation of a polyalkenyl derivative of a monoethylenically unsaturated C.sub.4 -C.sub.10 dicarboxylic acid material wherein the ratio of dicarboxylic acid moieties per polyalkenyl chain is less than 1.2:1. That process comprises reacting a polyalkene having a Mn in the range of 950 to 5000 with a monoethylenically unsaturated C.sub.4 -C.sub.10 dicarboxylic acid material in a mole ratio of greater than 1:1 at a temperature in the range of 1500 to 260.degree. C. in the presence of a polyaddition-inhibiting amount of a sulfonic acid.
In all of these applications, the sulfonic acid is added at the beginning of the reaction.